The purpose of this investigation is to study the relationships between facial height; positioning of the mandible by the muscles of mastication, vertical lip, tongue and occlusal forces; and tooth eruption. These relationships will be investigated in human children who exhibit normal face height, as well as children who are developing long and short face vertical dyplasias. This will be accomplished by means of radiographic analyses, conventional intraoral transducers, and newly designed thin piezoelectric transducers which measure occlusal force. In addition, the effect of nasal vs oral respiration on mandibular positioning will be investigated. This information should not only better define these relationships, but offer insight for better recognition of eventual modification of these relationships.